This invention concerns the use of surface modified, silicate based hollow microspheres as fillers in various composite systems. In particular, this invention comprises the addition of a slurry of said microspheres and salts of a multivalent metal to certain organic polymer systems and to cements and the like, and then setting the system with the hollow microspheres present as a lightweight filler.
U.S. Pat. No. 4,340,642 and U.S. patent application Ser. No. 382,826 now U.S. Pat. No. 4,411,847 describe a method of improving the water resistance of non-fused, silicate based hollow microspheres by modifying their surfaces with suitable multivalent metal ions. These microspheres are altered by contacting slurries of said microspheres with the appropriate metal salt such as AlCl.sub.3 or Al.sub.2 (SO.sub.4) while controlling the pH. The microspheres are recovered from the slurry, washed and dried. These salt free, dried microspheres are required for polymer systems that are sensitive to salts or anions when they are being processed. The washing and drying steps are expensive and require additional time and energy.
It is an object of this invention to use multivalent metal modified microspheres as fillers in various polymer systems without washing or drying steps.